The invention is directed to devices for enhancing the growth and form of plant seedlings.
Within the past two decades, plant seedling growth enhancers (hereinafter referred to as "grow tubes") have been developed and used to assist newly planted seedlings to survive and grow at an enhanced rate and improved form during the early stages after planting. Seedling growth enhancers have found their greatest application to date in the forest industry, but have also been advantageously applied to other types of seedlings such as grape vine seedlings.
Conventional grow tubes are made by extruding thermoplastic into a desired profile and cutting the extrusion to desired lengths. This is a satisfactory approach to manufacture provided the profile is a configuration capable of being extruded, such as cylindrical grow tubes. However, it is not possible to extrude profiles that are nonlinear (i.e., those having other than straight longitudinal lines) or those having complex or other irregular configurations.
In the recent past grow tubes have been manufactured by thermoforming, in which a blank sheet of thermoplastic is placed over a mold or between mold halves, brought to temperature and then forced against the mold, such as by vacuum or compression between the mold halves. Using this method, irregular and nonlinear configurations having different advantages may be obtained.
Since grow tubes are typically cylindrical in form, the conventional approach using thermoforming is to mold them in split cylindrical halves and either fasten the halves along both pairs of adjacent edges, or to form a continuous hinge along one common edge and to fasten them at the opposite edge in clam-shell fashion.
There are a number of disadvantages with this approach, not the least of which is the amount of "draw" of the thermoplastic blank sheet into the mold. Stated otherwise, in order for the grow tube to be of a useful diameter, the split halves have a depth corresponding to at least the radius of the tube, requiring a relatively deep draw of the blank thermoplastic sheet. This can cause problems with formation of the desired configuration as well as over thinning of the material itself.
Another problem with this conventional approach is the lack of stiffness in the resulting grow tube, which adversely affects its stability in the field. In other words, the sides of a grow tube manufactured in this manner may be excessively flexible and/or subject to being pushed in when installed or in use.
The inventive grow tube is a result of an endeavor to utilize thermoforming while at the same time producing an improved structure that will stand up to the rigors of installation and use as well as to perform advantageously in enhancing seedling growth. We have found that these objectives may be attained by thermoforming a grow tube that has at least three segmented sides or lobes, preferably with each of the sides or lobes having a radius of curvature that is less than the effective radius of curvature of the tube itself. Stated otherwise, each of the individual lobed segments is arcuately formed and actually defines a concave recess relative to the effective radius of curvature of the tube itself. This represents an advantage from the standpoint of thermoforming because the depth of each of the lobed segments is less than the depth of a half cylinder. Further, the lobed approach actually creates additional volume within the grow tube based on the radius of curvature of each of the lobed segments, giving the plant more room to grow.
In addition, the use of at least three lobed segments produces a grow tube that is more easily installed around an existing seedling. In the preferred embodiment, the three lobes are joined by a continuous integral hinge along two common edges, and fastening means are molded on the remaining edges enabling the device to easily be snapped into place in surrounding relation to a seedling. The use of at least three lobed segments with integral hinges also ensures that the fastening means will be in alignment as the free edges are brought together for fastening. Further, providing a releasable common edge or seam enables the grow tube to be installed around seedlings having growing branches or a larger crown without damage, as occurs when a closed cylindrical grow tube is installed by insertion over the top of the seedling.
The fastening means preferably are releasable and take the form of integrally molded snaps spaced along the two opposed open edges. This is not only advantageous from the standpoint of assembling and installing the grow tube in the field, but also permits access to the seedling as it grows for maintenance purposes. Specifically, one or more of the releasable snapping means in the middle of the grow tube may be unsnapped, and the opposing edges thereafter spread apart to gain access to the seedling. This does not otherwise disturb the grow tube itself or its stable installation.
With at least three joined common edges, the grow tube has superior strength and rigidity based on the fact that its fundamental cross sectional construction is that of a triangle. This rigidity is enhanced by tapering each open end inwardly and coupling this with a reversed flange. The reversed flange on the lower end is placed on top of the ground with earth in surrounding relation to the seedling mounded around it. The reversed flange on the upper end of the tube prevents abrasion to or cutting of the seedling as it grows beyond the top of the grow tube.
In addition, each of the lobed segments is formed with a plurality of tightly spaced corrugations that extend transversely to the axis of the grow tube. These corrugations provide additional stiffness, and also give rise to a faceted inner surface that serves to reflect external light received into the tube, reflecting and scattering it multidirectionally to optimize light exposure to the seedling.
The fact that the grow tube of the preferred embodiment includes three lobed segments rather than two gives it the inherent strength of a triangle, providing stiffness as well as resistance to collapse from external forces. As a result, the installed grow tube fully protects the seedling it surrounds with strength and stability, prevents damage to the seedling by animals, sprayed herbicides and the like, and creates an internal microenvironment that enables the seedling to grow and flourish in its early stages of formation.